One half the -rays from a 99mTc sample are absorbed by a 0.170-mm-thick lead shielding layer. Half of the -rays that pass through the first layer of lead are absorbed in a second layer of equal thickness. What thickness of lead will absorb all but one in of these -rays?
A 2.00-cm-thick sodium-iodide crystal absorbs all but of rays from a radioactive source. What percentage of rays will not be absorbed by 4.00-cm thickness of the same material?